Numerous rolls rotatably supported using bearings are used in an iron mill, a paper-making mill, etc. In each of such mills, the lives of the bearings are monitored and diagnosed using vibration sensors or the like, a component replacement plan is made, estimate is requested to be prepared by a bearing manufacturer, and an order is placed. However, in the diagnosis in a mill not specialized in bearings, it may be difficult to accurately diagnose the lives of the bearings in some cases because of problems in facilities and technology, and it is general that numerous bearings for replacement are in stock against sudden accidents. Furthermore, the bearing manufacturer needs to prepare a large amount of stock and many salespersons so as to be ready for significant change in the amount of orders and for sudden orders received.
For the purpose of solving these problems, a monitoring/diagnostic system and a method therefor are provided in which a sensor is mounted on a bearing used by a user to measure the vibration waveform, temperature, images, etc. of the bearing, and the states of the bearing are monitored by catching the signal transmitted from the sensor at a remote location, and the life of the bearing is diagnosed by a bearing manufacturer at the remote location (for example, see Patent document 1). According to Patent document 1, in the case that the state of a bearing in the early stage of abnormality is detected, the machine is stopped before the damage of the bearing becomes extensive, thereby preventing adverse effects to products to be produced and preventing serious damages to attached facilities, and the bearing to be replaced is ordered early so that the replacement can be carried out smoothly, and furthermore the number of bearings required to be replaced is optimized to improve the efficiency in inventory management.
In addition, when fatigue occurs in a bearing material, changes occur in the texture of the bearing material, such as the transformation of residual austenite into martensite, the decrease in dislocation density and the increase in compressive residual stress. As a technology for predicting the fatigue progression of a bearing, a technology in which the fatigue progression is predicted by measuring changes in the texture using X-rays has been devised (for example, see Patent document 2). Furthermore, a technology is known in which the fatigue degree of a test object, not a bearing, made of austenitic stainless steel is predicted by measuring, using an eddy current, the change in the magnetic permeability caused by the change from the austenite phase to the martensite phase due to working transformation (for example, see Patent document 3). Moreover, a bearing load state diagnostic method is known in which the decreased amount of residual austenite is measured using an eddy current (for example, see Patent document 4).